1. Field of the Invention
The present invention relates to a rewritable bar code display medium, an image display method using the rewritable bar code display medium, and an apparatus for implementing the image display method.
The bar code display medium of the present invention can form a bar code thereon, which bar code includes a two-dimensional bar code for general use, and other optical recognition patterns represented by an optical character recognition (OCR) pattern or a code consisting of four distinguishable areas, capable of representing sixteen different types of information in total.
2. Discussion of Background
Bar code display is widely applied to the point of sale (POS) system. There are two methods for bar code displaying for commercial products in the POS system. One is a so-called source marking method, in which a commercial code is printed in the form of a bar code and attached to each commercial product by the manufacturer in advance, and the other method is a so-called in-store marking method in which a commercial code is printed in the form of a bar code and attached to each commercial product at the retail sale stage. The bar codes of this kind for this method can be printed with high accuracy, but are not suitable when the manufacturer produces a wide variety of products, each in a small amount. The in-store marking method is particularly used for perishable foods in ordinary stores, and for controlling a variety of automobile parts in the factories of automobiles.
To print a bar code for use in the above-mentioned in-store marking method, a thermosensitive recording paper or a thermal image transfer ink ribbon is generally used as described in "Automation Technology" Tanaka, vol. 17, 6, p.109 1985. The bar coded printed on such a conventional recording paper or by use of such an ink ribbon bar is not rewritable. Therefore, for instance, when the price of a commercial product is changed, there is no choice but remove the old bar code label and instead attach a new bar code label carrying updated information to the product, or attach a new bar code label over the old bar code label. Further, when the bar code is utilized for a control system, new information cannot be added to the original bar code at each process in the control system, although a new lot number may be added by using a new bar code label.
Furthermore, bar codes printed on a thermosensitive recording paper are so poor in durability that they fade when exposed to ultraviolet light and chemicals.
Furthermore, since the surface of the thermosensitive recording paper is generally rough, the boundaries between printed bar code image areas and non-image areas (background) are not so sharp that it is extremely difficult to form bar code images with high accuracy and high resolution.
In the case where a bar code image is thermally transferred to an image-receiving sheet by using a thermal image transfer ink ribbon, it is difficult to uniformly transfer an ink layer of the thermal image transfer ink ribbon to the image-receiving sheet, so that the image density of printed bar codes becomes uneven particularly in the edge portions of the image areas or the ink is not transferred accurately imgewise, thus it is difficult to produce bar code images with high accuracy and high resolution.
As mentioned above, the conventional bar code images which are not produced by a printing method are not satisfactory with regard to the resolution, density, and accuracy because the boundaries between a bar code image area and a non-image area (background) are not clear cut. Therefore, such bar code images are not always read accurately by a bar code reader with sufficiently high reliability at present.